[PATCH] selftests/vfio: avoid VLAs

[Alex Mastro]

Allocate VFIO ioctl requests dynamically instead of using VLAs. GCC 11.5.0
rejects initialized VLAs with:

  error: variable-sized object may not be initialized

The replaced stack u8 arrays also do not guarantee native struct alignment
for the aliased pointers.

Fixes: 19faf6fd969c ("vfio: selftests: Add a helper library for VFIO selftests")
Fixes: 20face8c75ff ("vfio: selftests: Add helper to set/override a vf_token")
Signed-off-by: Alex Mastro <amas...@fb.com>
Assisted-by: Codex:gpt-5.5-high
---
 tools/testing/selftests/vfio/lib/vfio_pci_device.c | 28 +++++++++++++---------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c 
b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
index 94dc5fcecbeb..0b437435cce1 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -30,13 +30,12 @@
 static void vfio_pci_irq_set(struct vfio_pci_device *device,
                             u32 index, u32 vector, u32 count, int *fds)
 {
-       u8 buf[sizeof(struct vfio_irq_set) + sizeof(int) * count];
-       struct vfio_irq_set *irq = (void *)&buf;
-       int *irq_fds = (void *)&irq->data;
+       struct vfio_irq_set *irq;
+       size_t irq_size = sizeof(*irq) + sizeof(int) * count;
 
-       memset(buf, 0, sizeof(buf));
-
-       irq->argsz = sizeof(buf);
+       irq = calloc(1, irq_size);
+       VFIO_ASSERT_NOT_NULL(irq);
+       irq->argsz = irq_size;
        irq->flags = VFIO_IRQ_SET_ACTION_TRIGGER;
        irq->index = index;
        irq->start = vector;
@@ -44,12 +43,13 @@ static void vfio_pci_irq_set(struct vfio_pci_device *device,
 
        if (count) {
                irq->flags |= VFIO_IRQ_SET_DATA_EVENTFD;
-               memcpy(irq_fds, fds, sizeof(int) * count);
+               memcpy(irq->data, fds, sizeof(int) * count);
        } else {
                irq->flags |= VFIO_IRQ_SET_DATA_NONE;
        }
 
        ioctl_assert(device->fd, VFIO_DEVICE_SET_IRQS, irq);
+       free(irq);
 }
 
 void vfio_pci_irq_trigger(struct vfio_pci_device *device, u32 index, u32 
vector)
@@ -118,15 +118,21 @@ static void vfio_pci_irq_get(struct vfio_pci_device 
*device, u32 index,
 static int vfio_device_feature_ioctl(int fd, u32 flags, void *data,
                                     size_t data_size)
 {
-       u8 buffer[sizeof(struct vfio_device_feature) + data_size] = {};
-       struct vfio_device_feature *feature = (void *)buffer;
+       struct vfio_device_feature *feature;
+       size_t feature_size = sizeof(*feature) + data_size;
+       int ret;
 
+       feature = calloc(1, feature_size);
+       VFIO_ASSERT_NOT_NULL(feature);
        memcpy(feature->data, data, data_size);
 
-       feature->argsz = sizeof(buffer);
+       feature->argsz = feature_size;
        feature->flags = flags;
 
-       return ioctl(fd, VFIO_DEVICE_FEATURE, feature);
+       ret = ioctl(fd, VFIO_DEVICE_FEATURE, feature);
+       free(feature);
+
+       return ret;
 }
 
 static void vfio_device_feature_set(int fd, u16 feature, void *data, size_t 
data_size)

---
base-commit: a26b499b757cfc8bbff1088bb1b844639e250893
change-id: 20260612-scratch-amastro-vfio-selftests-avoid-vlas-395eb3dcb3ab

Best regards,
--  
Alex Mastro <amas...@fb.com>